Display devices in which light propagated by a waveguide is extracted from a lateral face of the waveguide are disclosed in JP H7-287176A (particularly pages 6-7 and FIGS. 1 to 20) and JP H11-202222A (particularly pages 3-4, paragraph (0010), and FIG. 2) for example. These display devices are provided with actuator portions that are connected to light extraction portions and made of a ceramic piezoelectric film. Rest and displacement of the actuator portion is carried out by applying a voltage to the actuator portion such that the light extraction portion comes in contact with or moves away from the light waveguide, thereby extracting leakage light in a controlled manner.
Display devices that use the above system have been implemented as large size display panels. A commercialized example of these is presented in a CeramVision/CeramBoard brochure (fifth page, lower left column) at the following Internet address: http://www.ngk.co.jp/ELE/product/07/index.html (accessed on Jul. 25, 2002).
With traditional displays, light that is totally reflected and propagated within the waveguide is made to leak to the outside from a lateral face of the waveguide by bringing the waveguide and the light extraction portion together to a distance less than the wavelength of the light. That is, so called evanescent waves are extracted (particularly see paragraph (0009) of JP H7-287176A and claim 1 of JP H11-202222A). As shown in drawings such as FIGS. 1 and 4 of JP H7-287176A, the extraction of light from a lateral face of the waveguide is controlled by whether or not a flat surface of a displacement transmission portion (light extraction portion) is made to come into contact with a planar waveguide.
Furthermore, FIG. 3 of JP H11-202222A shows the transmissivity of light when evanescent light of light that is totally reflected by a total reflection surface is extracted at an extraction surface that has been brought in to proximity with the total reflection surface. According to this, transmissivity of approximately 50% is shown for light that has an incident angle in the range of 50° to 80° to the total reflection surface when the distance between the total reflection surface and the extraction surface is in the range of 0.1 to 0.05 μm.
Furthermore, for example, a display device is disclosed in “Waveguide Panel Display Using Electromechanical Spatial Modulators,” X. Zhou, E. Gulari, SID98 Digest, 1998, pages 1,022 to 1,025, in which an electrostatic actuator, in which a metal electrode film is formed on a polyimide film, is used as the actuator portion and an LED is used as the light source. In this display device, in contrast to the light extraction portion's width of 0.23 mm, the thickness of the waveguide is 0.5 mm. Furthermore, a surface of the waveguide is an ITO film, and the surface of the light extraction portion that comes into contact with the ITO film is made by forming a film doped with titanium dioxide particles, which affect the diffusion properties of the polyimide, on an electrode, such that this film becomes a composite material harder than polyimide.
The above-described conventional display device has low efficiency in extracting from the waveguide the light that is propagated in the waveguide. Moreover, unless the light extraction portion exerts a large pressure on the waveguide, the extracted light has insufficient brightness and is uneven.